The invention generally relates to roll apparatus for treating a web of material and more particularly to a temperature sensor for measuring the temperature of the outer rotating surface of the roll.
The exact determination of the temperature of roll surfaces in operation has been a longstanding problem in the paper, textile, and plastic industries. There are in principle several possibilities for temperature measurement. One possibility is to provide a suitable sensor that rotates with the roll and to derive the measured temperature values of the rotating roll through wiper contacts. Apart from the considerable expense, a disadvantage of this form of sensor lies in that only the temperature at a certain point can be picked up and, in particular, placing the sensor in the roll surface creates an inhomogeneity which in most cases is not acceptable because, for example, marks will appear on the paper web. Another possibility is to provide temperature measuring elements, fixedly disposed on the roll surface that make sliding or rolling contact with the roll surface. This type of sensor results in inaccurate temperature measurement, leads to early wear of the temperature measuring element and produces marks on the roll. Lastly, in another possibility, the temperature of roll surfaces can be determined with radiation pyrometers. This type of temperature measurement is currently practiced to a larger degree than the previously mentioned possibilities. Radiation pyrometers can sense temperatures without roll contact at any point on the roll and at relatively low cost, but are subject to imprecision if the emission factor of the roll surface changes in an uncontrolled manner. This can occur, for example, due to moisture influences of various kinds or because the roll tarnishes, as may be the case with use of highly heated rolls commonly used in the nonwoven textile and plastics industries.
In DE-OS No. 14 98 490 a temperature measuring device for running webs is disclosed that comprises, for example, a, tubular housing with a surface provided at the end disposed toward the fabric that forms with the web, for example, a wedge-shaped space that narrows in the running direction of the web. In the housing surface, openings are provided for passage of the air boundary layer, located directly at the web surface, to the temperature sensor contained inside the tubular housing. The temperature sensor is formed by a thermocouple. The air boundary layer, which is entrained by the web and has the same temperature as the web, is trapped in tee wedge-shaped space and conducted through the openings into the interior of the housing. In the housing interior, a relatively undisturbed measuring of the temperature can take place. This temperature measuring device would not be very suitable for use on roll surfaces because as the roll rotates the same area on the roll surface would run past the temperature measuring device and the boundary layer disturbed by the temperature measuring device could not reestablish itself for further temperature measurement in only one revolution of the roll.
In DE-PS No. 26 50 771 an apparatus is disclosed for measuring the temperature of a surface of a rotating roll having a temperature sensor directed against the roll and a belt disposed between the roll and the sensor that abuts against the roll in a looping region and is movable in a longitudinal direction in a plane perpendicular the axis of the roll. This apparatus is used for measuring the temperature of a heated melt-on roll in a melt fixing system for the melting of toner images on a support material. In this patent a cleaning belt, which is for wiping entrained toner off the roll surface, abuts against the roll. A temperature sensor in the form of a thermocouple formed by two metal belts butt-welded together abuts against the cleaning belt on the side away from the roll surface. The weld point is pressed against the cleaning belt and the roll surface by an elastic cushion. The lo cleaning belt is wound intermittently from a supply spool onto a take-up spool.
For rolls used in the paper, textile and plastics industries, i.e., rolls which are not used in copying devices, but serve to imprint and possibly to heat-treat wide fabric webs running over the rolls, a cleaning belt to be wound from a supply spool onto a take-up spool cannot be provided. If the temperature sensor were used without the cleaning belt, the thermocouple would slide directly over the roll surface and short-circuit the thermocouple. Also the thermocouple would o wear quickly and the problems caused by marks appearing on the roll surface would occur.
The invention is directed to the problem of providing an improved apparatus for measuring the temperature of a surface of a rotating roll used in paper, textile and plastic treating that can measure temperature accurately at relatively low cost without the occurrence of frictional wear on the apparatus and/or marks on the roll.